When constructing offshore production platforms, it is necessary to transport the components forming the platforms from the place where they are manufactured to the offshore location of the platform. In general, the components will be manufactured at a site located very close to a coast, and it will be necessary to move these components over distances of approximately 250 meters from the site onto a barge. Once on the barge, the components will be transported to a predetermined offshore location where they will be upended and lowered into the sea at the appropriate position.
Generally, offshore production platforms are extremely large structures, components forming the platform can weigh as much as about 22,500 tons or more. There are thus special problems associated with moving such large structures from the site of manufacture to a barge. A known apparatus for moving a large component comprises a frame having a skid track along which the component is moveable, and a pulling unit. A plurality of steel cables, typically 50 strands each, are attached first to the component to be moved and secondly to the frame. The pulling unit pulls the strands which in turn causes the component to move towards the desired location. The pulling unit comprises means for repeatedly gripping and then pulling the strands as they pass through the frame.
A disadvantage of this known apparatus is that many connections are required between the component and the strands. This is time consuming and expensive and results in a complicated structure. A second disadvantage is that the strands must be cut to a predetermined length suitable for the particular component being moved. A third disadvantage is that the strands must be cut to length, and it is therefore rarely possible to re-use the strands for a different job. A further disadvantage is the large elastic stretch which occurs when the strands are at high load; this large elastic energy results in highly dynamic initial movement of the structure. Additionally, each strand, wire or pull rod is under extreme tension and the failure of any one of them can be lethal.